Carbon nanotube modified lithium manganese iron phosphate material, and application and preparation method thereof

Abstract

The invention relates to the technical field of lithium batteries, in particular to a carbon nanotube modified lithium manganese iron phosphate material, application and a preparation method. The method comprises the following steps: mixing a solution containing lithium, phosphorus, iron and manganese with carbon nanotubes, heating to obtain lithium manganese iron phosphate powder, and sintering to generate the carbon nanotube modified lithium manganese iron phosphate material in situ. According to the method, the lithium manganese iron phosphate positive electrode material is generated in situ by utilizing the excellent conductivity of the carbon nanotubes, and the carbon nanotubes can form a uniform conductive network, so that the internal resistance of the material is remarkably reduced, and the charge-discharge efficiency of the material is improved; the method is simple in preparation process, uniform in obtained material structure, low in production energy consumption and raw material cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and more particularly, to a carbon nanotube-modified lithium iron manganese phosphate material, its application and preparation method. Background Art

[0002] The energy density of lithium iron phosphate (LFP) batteries has approached the theoretical upper limit. Lithium iron manganese phosphate (LMFP) is regarded as an important upgrade direction for LFP batteries, and has significant improvements in aspects such as cycle life, cost, safety, and low-temperature performance. By introducing manganese elements, LMFP increases the voltage platform of the material, making its energy density 15%-20% higher than that of LFP. Although LMFP has a higher energy density and working voltage than LFP, it has the following pain points:

[0003] (1) Low electronic conductivity and low lithium ion diffusion rate;

[0004] (2) Small compaction density, which affects the exertion of energy density;

[0005] (3) The Jahn-Teller effect of Mn 3+ ;

[0006] Researchers have found that the conductive performance can be improved by surface coating with carbon materials to reduce the manganese dissolution during charge and discharge. However, the effect of conventional surface coating is usually limited by the uniformity and thickness of the coating layer. An overly thick coating layer may hinder the diffusion of lithium ions. In addition, the coating effect may also be limited by the integrity and stability of the coating layer. In some cases, the coating layer may be penetrated by the electrolyte, resulting in side reactions. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a carbon nanotube-modified lithium iron manganese phosphate material, its application and preparation method.

[0008] The technical solution of the present invention to solve the above technical problem is as follows:

[0009] The present invention provides a preparation method of a carbon nanotube-modified lithium iron manganese phosphate material. A solution containing lithium, phosphorus, iron, and manganese is mixed with carbon nanotubes and heated to obtain lithium iron manganese phosphate powder, and then sintered to in-situ generate the carbon nanotube-modified lithium iron manganese phosphate material.

[0010] On the basis of the above technical solution, the present invention can be further improved as follows.

[0011] Further, it includes the following steps:

[0012] S1. Prepare a lithium source solution and a phosphorus source solution respectively, and drop the phosphorus source solution into the lithium source solution to obtain a first mixed solution;

[0013] S2. Prepare an iron source solution and a manganese source solution respectively, and mix the iron source solution and the manganese source solution to obtain a second mixed solution;

[0014] S3. Drop the second mixed solution into the first mixed solution, and then add carbon nanotubes to obtain a third mixed solution;

[0015] S4. Heat and react the third mixed solution to obtain a reactant;

[0016] S5. Wash, dry and grind the precipitate in the reactant to obtain the lithium iron manganese phosphate powder;

[0017] S6. Sinter the lithium iron manganese phosphate powder to obtain the carbon nanotube-modified lithium iron manganese phosphate material.

[0018] Further, in step S1, the solute of the lithium source solution is a lithium source component, the solvent is a mixed solution of ethylene glycol and water, and the lithium source component is at least one of lithium carbonate, lithium acetate, lithium hydroxide, and lithium dihydrogen phosphate; the solute of the phosphorus source solution is a phosphorus source component, the solvent is ethylene glycol, and the phosphorus source component is at least one of phosphoric acid, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate; the molar ratio of lithium to phosphorus is 1:1.

[0019] Further, in step S2, the solute of the manganese source solution is a manganese source component, the solvent is a mixed solution of ethylene glycol and water, and the manganese source component is at least one of manganese oxalate, manganese sulfate, and manganese acetate; the solute of the iron source solution is an iron source component, the solvent is ethylene glycol, and the iron source component includes at least one of ferrous oxalate, iron acetate, and ferrous sulfate; the molar ratio of the manganese source solution to the iron source solution is 5:5 to 9:1.

[0020] Further, in step S3, the mass percentage of the carbon nanotubes is 0.05 wt% to 2 wt% of the mass of lithium iron manganese phosphate theoretically generated from the raw materials.

[0021] Further, in step S4, the third mixed solution is introduced into a polytetrafluoroethylene inner liner, and heated and reacted in a sealed stainless steel environment to obtain the reactant. The temperature of the reaction is 160 to 200 °C, and the time of the reaction is 8 to 16 h.

[0022] Further, in step S6, the lithium iron manganese phosphate powder is mixed with a carbon source and then sintered. The carbon source is at least one of glucose, sucrose, and polyvinylpyrrolidone; the mass of the carbon source is 0 to 30 wt% of the mass of the lithium iron manganese phosphate powder.

[0023] Further, in step S6, the sintering conditions are annealing at a temperature of 500 to 700 °C for 1 to 6 h in an inert atmosphere.

[0024] The present invention also provides a lithium iron manganese phosphate material modified by carbon nanotubes, which is prepared by the method as described above.

[0025] The present invention also provides an application of the lithium iron manganese phosphate material modified by carbon nanotubes as described above, which can be used for preparing lithium batteries.

[0026] The beneficial effects of the present invention are as follows:

[0027] (1) For the preparation method of the lithium iron manganese phosphate material modified by carbon nanotubes of the present invention, by utilizing the excellent electrical conductivity of carbon nanotubes, the lithium iron manganese phosphate cathode material is in-situ generated. The carbon nanotubes can form a uniform conductive network, significantly reducing the internal resistance of the material, thereby improving the charge and discharge efficiency of the material.

[0028] (2) For the preparation method of the lithium iron manganese phosphate material modified by carbon nanotubes of the present invention, the in-situ generation method enables the carbon nanotubes and the lithium iron manganese phosphate particles to be tightly combined, enhancing the electron transfer efficiency and improving the discharge specific capacity of the material.

[0029] (3) For the preparation method of the lithium iron manganese phosphate material modified by carbon nanotubes of the present invention, the preparation process is simple, the obtained material has a uniform structure, low production energy consumption and raw material cost, and is suitable for large-scale industrial production.

[0030] (4) The lithium iron manganese phosphate material modified by carbon nanotubes of the present invention has a lower internal resistance and good charge and discharge efficiency, and also has a good discharge specific capacity. Description of the Drawings

[0031] Figure 1 It is a schematic diagram of the preparation process of Example 1 for the preparation method of the lithium iron manganese phosphate material modified by carbon nanotubes of the present invention;

[0032] Figure 2 It is a SEM image of Example 1 for the preparation method of the lithium iron manganese phosphate material modified by carbon nanotubes of the present invention;

[0033] Figure 3 It is a PXRD diagram of the materials prepared in Example and Comparative Example for the preparation method of the lithium iron manganese phosphate material modified by carbon nanotubes of the present invention;

[0034] Figure 4 It is a cyclic stability diagram of the materials prepared in Example and Comparative Example for the preparation method of the lithium iron manganese phosphate material modified by carbon nanotubes of the present invention. Detailed Embodiments

[0035] The principles and features of the present invention are described below with reference to the drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0036] The preparation method of the carbon nanotube-modified lithium iron manganese phosphate material of the present invention is to mix a solution containing lithium, phosphorus, iron and manganese with carbon nanotubes and heat to obtain lithium iron manganese phosphate powder, and then sinter it to in-situ generate the carbon nanotube-modified lithium iron manganese phosphate material.

[0037] The preparation method of the carbon nanotube-modified lithium iron manganese phosphate material of the present invention, relying on the excellent conductivity of carbon nanotubes, when in-situ generating the lithium iron manganese phosphate cathode material, the carbon nanotubes can form a uniform conductive network, significantly reducing the internal resistance of the material, thereby improving the charge and discharge efficiency of the material; the in-situ generation method enables the carbon nanotubes and lithium iron manganese phosphate particles to be tightly combined, enhancing the electron transfer efficiency and increasing the discharge specific capacity of the material.

[0038] The preparation method of the carbon nanotube-modified lithium iron manganese phosphate material of the present invention is prepared by using an in-situ generation technology, which effectively simplifies the production process, reduces the non-uniformity that may occur in the traditional method, and at the same time makes the preparation process easy to control, with low energy consumption and raw material costs, and is suitable for large-scale industrial production.

[0039] Preferably, in the carbon nanotube-modified lithium iron manganese phosphate material of the present invention, the chemical formula of lithium iron manganese phosphate conforms to LiFe 0.2 Mn 0.8 PO 4 。

[0040] Specifically, the preparation method of the carbon nanotube-modified lithium iron manganese phosphate material of the present invention includes the following steps:

[0041] S1. Prepare a lithium source solution and a phosphorus source solution respectively, and drop the phosphorus source solution into the lithium source solution to obtain a first mixed solution;

[0042] Preferably, the solute of the lithium source solution is a lithium source component, the solvent is a mixed solution of ethylene glycol and water, and the lithium source component is at least one of lithium carbonate, lithium acetate, lithium hydroxide, and lithium dihydrogen phosphate; the solute of the phosphorus source solution is a phosphorus source component, the solvent is ethylene glycol, and the phosphorus source component is at least one of phosphoric acid, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate; the molar ratio of lithium to is 1:1.

[0043] S2. Prepare an iron source solution and a manganese source solution respectively, and mix the iron source solution and the manganese source solution to obtain a second mixed solution;

[0044] Preferably, the solute of the manganese source solution is a manganese source component, the solvent is a mixed solution of ethylene glycol and water, and the manganese source component is at least one of manganese oxalate, manganese sulfate, and manganese acetate; the solute of the iron source solution is an iron source component, the solvent is ethylene glycol, and the iron source component includes at least one of ferrous oxalate, iron acetate, and ferrous sulfate; the molar ratio of the manganese source to the iron source is 5:5 to 9:1.

[0045] In the mixed solution of ethylene glycol and water used in the above steps S1 and S2, the volume ratio of ethylene glycol to water is 1:10.

[0046] In the above steps S1 and S2, the specific dosages of the lithium source solution, the phosphorus source solution, the iron source solution, and the manganese source solution should conform to the contents of each element in LiFe 0.2 Mn 0.8 PO 4 .

[0047] S3. Drop the second mixed solution into the first mixed solution, and then add carbon nanotubes to obtain a third mixed solution; the mass percentage of the carbon nanotubes is 0.05 wt% to 2 wt% of the mass of the lithium iron phosphate manganese generated according to the raw materials theory.

[0048] It should be noted that in order to prevent the lithium source solution, the phosphorus source solution, the iron source solution, and the manganese source solution from being oxidized, in the foregoing steps, the steps of solution preparation and mixing are all carried out under an inert atmosphere.

[0049] Preferably, the carbon nanotubes are 3D carbon nanotubes; the 3D carbon nanotubes can be evenly distributed inside the lithium iron phosphate manganese matrix and form a three-dimensional conductive network structure, improving the electron transport ability and structural stability of the material.

[0050] Preferably, before use, the carbon nanotubes are pretreated. After the pretreated carbon nanotubes are added, they can be evenly dispersed in the ethylene glycol solution under high-temperature conditions, facilitating the in-situ growth of lithium iron phosphate manganese subsequently.

[0051] Preferably, the pretreatment is as follows: using ethylene glycol as a solvent, adding the carbon nanotubes to ethylene glycol, and adding them to a polytetrafluoroethylene inner liner, keeping the temperature at 180 °C for 5 h, filtering by suction, drying, and setting aside.

[0052] S4. Heat and react the third mixed solution to obtain a reactant.

[0053] Preferably, the third mixed solution is introduced into a polytetrafluoroethylene inner liner, heated and reacted in a sealed stainless-steel environment to obtain a reactant, the reaction temperature is 160 - 200 °C, and the reaction time is 8 - 16 h.

[0054] S5. Wash, dry, and grind the precipitate in the reactant to obtain lithium iron phosphate manganese powder.

[0055] Preferably, the washing method is to wash the precipitate with deionized water and ethanol alternately by suction filtration or centrifugation, and the number of washing times is 3 - 6 times.

[0056] Preferably, the drying conditions are drying at 60 - 120 °C for 12 - 24 h.

[0057] S6. Sinter the lithium iron manganese phosphate powder to obtain a carbon nanotube-modified lithium iron manganese phosphate material.

[0058] Preferably, the lithium iron manganese phosphate powder is mixed with a carbon source and then sintered. The carbon source is at least one of glucose, sucrose, and polyvinylpyrrolidone; the mass of the carbon source is 0-30 wt% of the mass of the lithium iron manganese phosphate powder.

[0059] Preferably, the sintering conditions are annealing at a temperature of 500-700 °C for 1-6 h in an inert atmosphere; these reaction conditions can prevent the oxidation of ferrous salts and the oxidation of the product, which may affect the material properties.

[0060] More preferably, the inert atmosphere is a mixed gas of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 95:5.

[0061] The carbon nanotube-modified lithium iron manganese phosphate material of the present invention is prepared by the method as described above. This material has a lower internal resistance, good charge and discharge efficiency, and good discharge specific capacity.

[0062] The carbon nanotube-modified lithium iron manganese phosphate material of the present invention can be used to prepare lithium batteries; specifically, the material can be used as the positive electrode material of lithium batteries, which can effectively improve the performance of lithium batteries.

[0063] The present invention is illustrated below by specific examples and comparative examples.

[0064] Example

[0065] As Figure 1 shown, in this example, the carbon nanotube-modified lithium iron manganese phosphate material is prepared by the method of the present invention, and the dissolution processes in steps (1)-(4) are all carried out in an inert gas atmosphere. The steps include:

[0066] (1) Weigh the Li source lithium hydroxide, the P source phosphoric acid, the Fe source ferrous sulfate, and the Mn source manganese sulfate according to the ratio.

[0067] (2) Dissolve lithium hydroxide in a mixed solution of 2 ml of water and 20 ml of ethylene glycol, disperse phosphoric acid in 15 ml of ethylene glycol, and add the phosphoric acid solution dropwise to the lithium hydroxide solution to obtain a first mixed solution.

[0068] (3) Dissolve ferrous sulfate in 10 ml of ethylene glycol solution, dissolve manganese sulfate in a mixed solution of 3 ml of water and 10 ml of ethylene glycol, and mix the ferrous phosphate solution and the manganese sulfate solution evenly to obtain a second mixed solution.

[0069] (4) Add the second mixed solution dropwise to the first mixed solution, and then add 0.2 wt% CNTs that have been pretreated, and stir evenly to obtain a third mixed solution.

[0070] (5) Pour the third mixed solution into a 100 ml polytetrafluoroethylene liner, seal it in a stainless steel autoclave, place it in a muffle furnace, and keep it at 180 °C for 10 h.

[0071] (6) Wash the precipitate 3 times with deionized water and ethanol respectively and perform centrifugation, then dry it at 80 °C. After grinding, lithium iron manganese phosphate powder CNTs-LFMP is obtained.

[0072] (7) Weigh 15 wt% of sucrose solution and mix it evenly with lithium iron manganese phosphate powder. Sinter it under the protection of a mixed atmosphere with an argon-hydrogen ratio of 95:5. The sintering condition is annealing at 650 °C for 2 h.

[0073] After cooling to room temperature and fine grinding, carbon nanotube modified lithium iron manganese phosphate material CNTs-LFMP / C is obtained.

[0074] Comparative Example

[0075] The difference between this comparative example and Example 1 is that CNTs are not added in step (4).

[0076] Perform performance tests on the materials prepared in the examples and comparative examples respectively. The specific test results are as Figures 1-3 shown and the specific analysis is as follows:

[0077] Figure 2 It is the SEM image of the sample prepared in the example. It can be seen that lithium iron manganese phosphate grows in-situ on the surface of carbon nanotubes, making the carbon nanotubes and lithium iron manganese phosphate particles closely combined, increasing the specific surface area of the material, accelerating the lithium ion transport rate, and at the same time facilitating the electrolyte to enter the secondary particles formed by aggregation, thereby improving the electrochemical performance of the material.

[0078] Figure 3 It is the PXRD patterns of the two samples prepared in the example and the comparative example. According to Figure 3 it can be seen that the diffraction peaks of the comparative example and the example are both close to the standard peaks of the orthorhombic olivine structure LiMnPO 4 (JCPDS 74-0375). The diffraction peak position of LMFP in the example is slightly positively shifted compared with that of pure LiMnPO 4 in the comparative example, indicating that Fe is successfully doped at the Mn site of LiMnPO 4 to form a solid solution material. No obvious impurity peaks and diffraction peaks of crystalline carbon are detected in the example, and the sample diffraction peaks are all sharp, indicating that the carbon in the material is amorphous, and the LMFP in the example has high purity and crystallinity.

[0079] Figure 4 It is the cyclic stability diagram of the two samples prepared in the example and the comparative example. According toFigure 4 It can be seen that within the voltage range of 2 - 4.5V and at the current density of charge and discharge at a rate of 1C, the capacity of the example remains at 116.9 mAh / g after 200 cycles. -1 , with a high capacity retention rate of 97.01%, which is significantly better than that of the comparative example. This shows that the example ensures the tight combination of carbon nanotubes and lithium iron phosphate manganese particles through in-situ growth, forming a uniform conductive network, and significantly improving the electron transport efficiency and structural stability of the material.

[0080] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0081] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a carbon nanotube-modified lithium manganese iron phosphate material, characterized in that: A solution containing lithium, phosphorus, iron and manganese is mixed with carbon nanotubes and heated to obtain lithium iron manganese phosphate powder, which is then sintered to in-situ generate the carbon nanotube-modified lithium iron manganese phosphate material.

2. The method for preparing a carbon nanotube-modified lithium manganese iron phosphate material according to claim 1, characterized in that: The following steps are involved: S1, preparing a lithium source solution and a phosphorus source solution respectively, and adding the phosphorus source solution dropwise into the lithium source solution to obtain a first mixed solution; S2, preparing an iron source solution and a manganese source solution respectively, and mixing the iron source solution and the manganese source solution to obtain a second mixed solution; S3, adding the second mixed solution dropwise to the first mixed solution, and then adding carbon nanotubes to obtain a third mixed solution; S4, heating the third mixed solution to react, to obtain a reactant; S5, washing, drying and grinding the precipitate in the reactant to obtain the lithium manganese iron phosphate powder; S6. Sintering the lithium iron manganese phosphate powder to obtain the carbon nanotube-modified lithium iron manganese phosphate material.

3. The method for preparing a carbon nanotube-modified lithium manganese iron phosphate material according to claim 2, characterized in that: In step S1, the solute of the lithium source solution is a lithium source component, the solvent is a mixture of ethylene glycol and water, the lithium source component is at least one of lithium carbonate, lithium acetate, lithium hydroxide, and lithium dihydrogen phosphate; the solute of the phosphorus source solution is a phosphorus source component, the solvent is ethylene glycol, and the phosphorus source component is at least one of phosphoric acid, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate; the molar ratio of lithium to phosphorus is 1:

1.

4. The method for preparing a carbon nanotube-modified lithium manganese iron phosphate material according to claim 3, characterized in that: In step S2, the solute of the manganese source solution is a manganese source component, the solvent is a mixture of ethylene glycol and water, and the manganese source component is at least one of manganese oxalate, manganese sulfate, and manganese acetate; the solute of the iron source solution is an iron source component, the solvent is ethylene glycol, and the iron source component includes at least one of ferrous oxalate, ferrous acetate, and ferrous sulfate; the molar ratio of the manganese source solution to the iron source solution is 5:5 to 9:

1.

5. The method for preparing a carbon nanotube-modified lithium manganese iron phosphate material according to claim 4, characterized in that: In step S3, the mass percentage of the carbon nanotubes is 0.05wt% to 2wt% of the mass of the lithium manganese iron phosphate theoretically generated from the raw materials.

6. A method for preparing a carbon nanotube-modified lithium manganese iron phosphate material according to any one of claims 2 to 5, characterized in that: In step S4, the third mixed solution is introduced into a polytetrafluoroethylene liner, heated and reacted in a sealed stainless steel environment to obtain the reactant, the reaction temperature is 160 to 200° C., and the reaction time is 8 to 16 hours.

7. A method for preparing a carbon nanotube-modified lithium manganese iron phosphate material according to any one of claims 2 to 5, characterized in that: In step S6, the lithium iron manganese phosphate powder is mixed with a carbon source and then sintered, wherein the carbon source is at least one of glucose, sucrose, and polyvinyl pyrrolidone; the mass of the carbon source is 0 to 30 wt % of the mass of the lithium iron manganese phosphate powder.

8. The method for preparing a carbon nanotube-modified lithium manganese iron phosphate material according to any one of claims 2 to 5, characterized in that: In step S6, the sintering conditions are: annealing at a temperature of 500 to 700° C. for 1 to 6 hours in an inert atmosphere.

9. A carbon nanotube-modified lithium manganese iron phosphate material, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. An application of the carbon nanotube-modified lithium manganese iron phosphate material as claimed in claim 9, characterized in that: Can be used to prepare lithium batteries.

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